What to put in a default label of a switch?

Question

Let's say I have an enumeration.

enum class ShapeName : char {TRIANGLE,CIRCLE,SQUARE};

and later I have a function like this:

void Function (ShapeName const shape){

    switch (shape){
        case ShapeName::TRIANGLE:
            DoSomething1();
            break;

        case ShapeName::CIRCLE:
            DoSomething2();
            break;

        case ShapeName::SQUARE: 
            DoSomething3();
            break;

        default:
            //THIS CODE BLOCK SHOULD NEVER BE EXECUTED!
    }

    return;
}

Although the default label should never be executed, I want to account for the potential bugs that may arise if a programmer adds another value to 'ShapeName' and it's not accounted for in the switch.
What would you recommended I do?

1. Assertions
I could use an assertion, but what am I asserting?

assert(false); //?

2. Exceptions
I could throw an exception, but I don't think that would be very good practice. I'm under the impression that exceptions are for run time events that can not be predicted because of certain environments.

3. Exits
I can just exit the program immediately with an error. That feels like the best idea, but I'm unsure if it's good practice. I thought the advantage of assertions was that you could turn them all off when you were ready ship the program. Then, all that assertion code would no longer exist.

---

Maybe there is another way that I'm not aware of. I do use a compiler flag that warns about unaccounted for values, but I still want to know what others recommend.

Answer 1

I like the idea of asserting with an informative message. Try this:

assert (!"The default case of so-so switch was reached.");

This always returns false, but provides a message you can use.

Edit:
I found the source I pulled this notion out of my memory from; it's in the following book:
C++ Coding Standards - 101 Rules and Guidelines